|  | 6.7 | Placing ACLs
| 6.7.3 | A firewall architecture to protect you from intruders

A firewall architecture is a structure that exists between you and the outside world to protect you from intruders. In most circumstances, intruders come from the global Internet and the thousands of remote networks it interconnects. Typically, a network firewall consists of several different machines. In this architecture, the router that is connected to the Internet (that is, the exterior router) forces all incoming traffic to go to the application gateway. The router that is connected to the internal network (that is, the interior router) accepts packets only from the application gateway. In effect, the gateway controls the delivery of network-based services both into and from the internal network. For example, only certain users might be allowed to communicate with the Internet, or only certain applications might be permitted to establish connections between an interior and exterior host. If the only application that is permitted is mail, then only mail packets should be allowed through the router. This protects the application gateway and avoids overwhelming it with packets that it would otherwise discard.
| Engineering Journal
| Using a Firewall Router